boat porpoising and X dimension

[dreamchaser]

need some xpert advise here.......hello all..... My boat has a 1983 115 rude ,its 19.5ft open centre consol i do have the motor mounted in the second to last hole from the top on the transom . When i power up with full trim in and bring it up to wot i can get 5800 rpm with a 19p 4 blade solas aluminum prop . then the moment i start to trim up the boat starts to bounce ....Ive been doin my research on X dimension and the way i understand it i need to lift motor yet shallower to change my thrust line to get above the centre of gravity therefore pushing bow down.......Am i on the right track?? i do have smart tabs installed as well tryin to dial them in as well. so far ive had them all the up and all the way in ...but they create a lot of resistance...i will keep playin with them and have a email sent to nauticus for help ....

 

[JB]

Re: boat porpoising and X dimension

Sounds like you are too high already, Chaser.

Porpoising is caused by too much bow lift. . . beyond the engine's ability to hold it up.

You didn't say anything about the anti-ventilation plate relative to the keel. Where is it? Is it parallel with the keel?

Do you have any setback on the engine?

From your description it sounds like you have optimum balance for plane with zero trim out. That is not going to give you optimum hole shot.

 

[QC]

Re: boat porpoising and X dimension

Yeah, I would try shifting some weight forward and at least try that. Definitiely, one change at a time though . . .

 

[dreamchaser]

Re: boat porpoising and X dimension

JB...... the leading edge of the ventilation plate is close to 1" above the keel at full trim in. There is no set back .... QC thought bout that possibly going to a smaller trolling motor ..I use a 1992 9.9 merc 2 stroke extra long leg kicker ...and the 1 battery thats in the opposite corner ....... thats it in the back

 

[WillyBWright]

Re: boat porpoising and X dimension

Trim tabs can eliminate that porpoising. So can a few sandbags in the bow. click

 

[tashasdaddy]

Re: boat porpoising and X dimension

i'd say you are stearn heavy with almost 400 lbs, hanging on the transom, i have an 18ft open center console, with a 1988 88 spl. it will porpose if i trim up to far.

 

[Jdeagro]

Re: boat porpoising and X dimension

Dreamchaser;

Before you make radical changes to the trim tab adjsutments and othe motor changes, Call me - 800-233-0194. Make sure you know where the adjsutments are now including the motor heght then call.

 

[Boomyal]

Re: boat porpoising and X dimension

Trim tabs can eliminate that porpoising. So can a few sandbags in the bow. click

Geeeeeeeez Willie, those things in your link are horrible. I got a set I'd donate for shipping costs, otherwize they are soon to go in the trash recyle. I rode those things from Marina Del Rey to Catalina Island. They'd like to have torn my boat apart.

On second thought, I'll put them on ebay. What'ya say, start the bidding at $.99 with $49.95 shipping and handling?8)

 

[dreamchaser]

Re: boat porpoising and X dimension

thks all for the ideas ...will be playin with set up of the tabs now ....keepin fingers crossed:d